This invention relates to ski goggles, and more particularly to a structure for preventing ski goggle lenses from fogging.
Since the ski goggles are used in a very cold climate as well known, the goggle lens is likely to fog up by virtue of the body temperature or perspiration of the skier during use, especially when the skier comes to a halt, possibly entailing an accident due to an obscured field of view. To prevent the goggle lens from fogging, it has been practice to
(1) subject the lens to a chemical antifogging surface treatment, or
(2) make the lens from a pair of inner and outer lens plates and form between the lens plates an interior space serving as a heat insulating layer.
These antifogging measures have advantages and disadvantages. The treatment (1) produces an appreciable antifogging effect when the goggle lens has a surface temperature of about 0.degree. C. or higher but is not fully effective in an environment in which the surface temperature drops to 0.degree. C. or a lower level since fog forming droplets of water will freeze on the surface of the goggle lens. In the case of the construction (2) in which the goggle lens comprises two lens plates and has an internal heat insulating space layer, the lens will not be fogged on its front side as by perspiration immediately after the skier comes to a halt but remains free from fog even when the front side lens surface has a temperature of 0.degree. C. or lower.
In order to protect the face for safety during skiing which is a hard exercise, goggle lenses of tough material such as plastics are widely used. Plastics goggle lenses nevertheless have the drawback that the variation in the pressure of the internal space of the lens due to an atmospheric pressure or temperature change during a descent deforms the lens plates and distorts the field of view through the lens. For example, when a goggle lens is used with its interior space sealed off at a great altitude, there arises a pressure difference between the inside and outside of the lens, subjecting the lens to compressive deformation in its entirety and giving a distorted field of view.
Accordingly goggle lenses have already been proposed which include an inner lens plate formed with an air port resembling a pinhole for maintaining the internal pressure of the lens in balance with the outside pressure to prevent the deformation of the lens. The air port formed in the inner lens plate, however, will permit the ingress of water (snow or the like) into the interior space of the lens, with the result that the water, when evaporating with an increase in temperature, fogs up the inside surfaces of the lens plates, rendering the goggle unserviceable as such.